Recent arrival A wrong turn mid-flight or a gust of wind, rather than geology, created the unique Tasmanian wedge-tailed eagle with a study showing it has a shorter connection to the Australian island than previously thought.

Genetic comparison of the Tasmanian sub-species and its mainland counterpart suggest the two species separated somewhere between 200 and 1000 years ago, says zoologist Dr Chris Burridge.

This overturns the long-held belief the sub-species was isolated about 13,000 years ago when Bass Strait flooded after the Last Glacial Maximum, the University of Tasmania researcher says.

Instead the Tasmanian population was established by individuals that flew across the Bass Strait.

The finding, published recently in Proceedings of the Royal Society B, has implications for conservation of the endangered Tasmanian wedge-tailed eagle, Aquila audux fleayi, and could lead to a rethink about the evolution of other island sub-species.

Burridge says island populations of animals and birds often differ from mainland relatives.

Slight differences

In the case of the Tasmanian wedge-tailed eagle, he says, they are darker in colour, have larger bodies, produce smaller clutches - one egg versus usually two on the mainland - and roost only in trees.

"It is commonly assumed that such differences developed following the complete isolation of populations by sea-level rise following the Last Glacial Maximum (LGM)," writes Burridge and his team.

"However, population divergence may predate the LGM, or marine dispersal and colonisation of islands may have occurred more recently; in both cases, populations may have also diverged despite ongoing gene flow."

To test these differing theories, Burridge and his colleagues genetically tested 224 individual birds - 49 from the mainland and 175 from Tasmania.

The sample included captive individuals, museum specimens, shed feathers and a Tasmanian Government frozen collection of deceased individuals gathered between 1996 and 2012.

Burridge says the analysis showed a "large genetic difference" between the Tasmanian and mainland wedge-tailed eagle but mostly due to "genetic variation that the Tasmanian sub-species lacks".

Using mitochondrial substitution rates - which measure how quickly genetic differences accumulate - the researchers determined the divergence between the two species happened between three to 95 years ago.

Settlers observed eagles

Burridge says this figure is an obvious underestimate because the substitution rate measure is "like timing a 100 metre sprint with an hourglass".

He says early observations from European settlers in the late 1700s suggest the wedge-tailed eagle was already in Tasmania and was widespread.

Tasmanian Aborigines also "seem to have a word that could apply to wedge-tailed eagles", he says adding to the evidence of a later isolation time than 100 years.

Burridge says it would seem likely the eagles separated from the mainland species between 200 and 1000 years.

He says the find shows it is no longer safe to assume the separation of the two land masses dates the divergence of species on a continental island, and its adjacent mainland and that where there is the possibility for air or marine dispersal genetic analysis is needed.

Burridge says the Tasmanian population has endangered species owing to its small size (1000-1500 birds in 426 breeding territories), loss and disturbance of breeding habitat, low reproductive success and high human-induced mortality.

He says introducing mainland wedge-tailed eagles onto the island could improve its reproductive success and fitness by increasing genetic diversity among the population.

"However you come up against people that believe it looks different and we should conserve that uniqueness," he says.

But Burridge cites the example of the Florida panther that was down to just tens of individuals when the decision was made to introduce the genetically different panthers.

"They brought in panthers from Texas and the reproductive success improved and the range of the species increased," he says.